Field of the Invention
The present invention relates to a wood type golf club head.
Description of the Related Art
Generally, a golf club head is believed to increase the back spin amount of a shot when the surface roughness of the face portion increases. A maximum distance performance-oriented wood type golf club head is known to be unable to obtain a long carry of a shot if the back spin amount of the shot is large. However, also known is that a long carry of a shot cannot be obtained if the back spin amount is too small. In the wood type golf club head, when forming grooves such as score lines in the face portion, the number of grooves tends to be relatively small. Additionally, in the wood type golf club head, the face portion is sometimes made thin to improve the coefficient of restitution of the face portion. However, the strength of the thin face portion may lower. Hence, there are proposed techniques of making grooves shallow for the purpose of preventing the strength of the face portion from lowering when forming grooves in the it (Japanese Patent Laid-Open Nos. 2003-299753 and 2002-153575 and U.S. Patent Application Publication Nos. 2003/0032498, 2004/0192465, and 2010/0009773).
On the other hand, in a golf club head having a relatively small loft angle (for example, 20° or less), the larger the surface roughness of the face portion is, the smaller the back spin amount may be. A golf club head described in Japanese Patent Laid-Open No. 2004-201787 is based on an idea of decreasing the surface roughness of the face portion at a position where the back spin amount decreases and increasing the surface roughness of the face portion at a position where the back spin amount increases. That is, the golf club head is based on the reverse of a general idea concerning the relationship between the roughness of the face portion and the back spin amount of a shot.
In a wood type golf club head represented by a driver or a spoon, since the loft angle is relatively small, the surface roughness of the face portion is preferably made large to decrease the back spin amount of a shot. As a method of adjusting the surface roughness of the face portion, a process such as sand blast or shot peening is known. However, to adjust the surface roughness of the face portion to a roughness suitable to suppress the back spin amount, the process may be difficult or may require effort. As another method of adjusting the surface roughness of the face portion, contriving score lines is considerable. However, in, for example, a golf club head for games, it may be difficult to adjust the surface roughness of the face portion to a roughness suitable to suppress the back spin amount in terms of conformity to rules (R & A rules).